Key to broach flag change with Queen

New Zealand's proposition to dump its flag is likely to be discussed when Prime Minister John Key and the Queen meet at Windsor Castle.

Mr Key was due to meet the monarch on Friday afternoon (local time), and told reporters he expected the possible flag change to come up.

However, he clearly did not believe it was a controversial topic, saying the Queen's position was that it was an issue for New Zealanders.

"That's the view the royal family's always taken when countries have raised a variety of constitutional matters, including some that have gone republic," Mr Key said.

"She's supportive of New Zealanders having a process if that's what they want to go through. I don't think you could say she would offer a view of whether they should do it or not."

Mr Key noted that he had previously raised the issue with the Queen, so he was likely to explain the referendum process the county was now taking.

Prior to his trip to Windsor, the Prime Minister was due to meet British Home Secretary Theresa May, while his evening included an informal dinner with his UK counterpart, David Cameron.

Discussion points are expected to include the New Zealand and European Union free trade agreement discussions, following Mr Key's meetings with the EU Commission and Council leadership in Brussels this week.

Mr Key also said he expected Britain's EU referendum and the forthcoming climate change summit in Paris to be raised.

"There'll be everything from politics to sport, I have no doubt, to economics," Mr Key said.

The Prime Minister will head to Twickenham on Saturday for the Rugby World Cup final before flying out of London that night.